Why is my aircon leaking water right after servicing?
A leak that starts after a service visit is rarely a coincidence, and it is rarely the part someone wants to replace. Three reassembly faults cause it. Where the water appears tells them apart.
By Team Snowflake | Updated 19 Aug 2026
1. Drain connection not fully reseated
A steady drip from one fixed point, with cooling unchanged, usually traces to a connection that was handled during the visit and not fully seated. A hose clip left half engaged, a fitting pushed on but not home, or a hose reconnected at an upward angle. Most water still clears, so the leak starts days later rather than the same evening.
How to tell
This path is a fixed weeping point rather than an overflow. Unlike a capped line, water still drains and the tray does not fill. Unlike open insulation, the drip sits at the unit instead of tracking along the trunking.
- Drip is slow but steady, always at the same spot.
- Cooling feels exactly the same as before the visit.
- The leak started days after the visit, not that evening.
- The flat had no history of leaking before.
How we confirm it
We trace the water back to the joint that is weeping, then reseat or re-angle that connection. A flush and a run under cooling load confirms the drip has stopped.
A leak near a condensate pump after a service visit is often quoted as a pump replacement. Replacing the pump does not fix a fitting that was left loose, so the leak comes back on the new part.
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2. Drain line left capped or obstructed
Water that pools and overflows, and gets worse the longer the unit runs, points to a drain path that is closed rather than loose. An outlet cap fitted during the work and not removed, or debris knocked into the line when a filter or panel came off. Light load still trickles through. Sustained cooling does not.
How to tell
This path is an overflow that builds with runtime. Unlike a loose connection, the water volume rises the longer the unit runs rather than weeping at a steady rate. Unlike open insulation, it stops building once the unit is switched off.
- Water backs up and spills rather than dripping steadily.
- It gets worse the longer the unit stays on.
- Switching the unit off stops the water building.
- Gurgling near the indoor unit before the overflow starts.
How we confirm it
We locate the restriction along the line and remove the cap or clear the obstruction. A sustained cooling run confirms the tray drains faster than it fills.
Do not keep running the unit while water is backing up. Overflow inside the casing reaches the control board, which turns a blocked drain into an electrical fault.
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3. Insulation or panel left open
Water appearing along the trunking, away from the unit body, usually means condensation is forming outside the drain path rather than escaping from inside it. Insulation opened during cleaning leaves a cold section exposed inside humid trunking. Moisture collects on that surface and runs out, while the drain itself passes water normally.
How to tell
This path forms outside the drain path. Unlike a loose connection, the drain tray passes water normally and flushing changes nothing. Unlike a capped line, the water tracks with humidity rather than with how long the unit has been running.
- Water shows along the trunking, not at the unit casing.
- Worse on humid days and after rain.
- Nothing spills from the front of the indoor unit.
- Flushing the drain makes no difference to the leak.
How we confirm it
We open the trunking run and find the exposed cold section, then re-insulate and reseal it. A run through a humid period confirms the sweating has stopped.
Repeated drain flushing will not fix this leak, because the water never enters the drain. If one flush has already changed nothing, the trunking route needs opening instead.
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4. Drain pan not reseated on its rails
Water running down the coil face and dripping from the bottom edge, rather than pooling anywhere, means the pan is catching nothing. The pan is lifted out for cleaning and has to go back on its guide rails. Sitting a few millimetres forward leaves a gap the condensate falls straight through.
How to tell
This path misses the drain completely. Unlike the other three, water never enters the drain path at all, so testing the line always shows it clear. The drip starts immediately rather than days later.
- Water runs down the face of the coil and drips off the bottom edge.
- It appears immediately, not days later.
- The drain itself flows normally when tested.
- The last visit was a deep clean rather than a filter wash.
How we confirm it
We remove and reseat the pan squarely on its guide rails, then run the unit under cooling load. The water is watched onto the pan to confirm nothing bypasses the lip.
Clearing the drain does not fix a pan that is out of position. The line was never blocked, so the flush changes nothing and the water keeps missing the pan entirely.
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